[math-fun] Q. about {0,1}-matrices.

Dear MathFun, SeqFans: Could anyone extend this sequence? %I A125587 %S A125587 1,4,68,5008 %N A125587 Call an n X n matrix robust if the top left i X i submatrix is invertible for all i = 1...n. Sequence gives number of n X n robust real {0,1}-matrices. %e A125587 a(2) = 4: %e A125587 10 10 11 11 %e A125587 01 11 01 10 %O A125587 1,2 %Y A125587 Cf. A125586. %K A125587 nonn,more %A A125587 njas and Vinay Vaishampayan (vinay(AT)research.att.com), Jan 05 2007 This "robust" property is relevant when doing an LU decomposition of a matrix, so it may have a more official name (besides "all principal submatrices are nonsingular", I mean). Neil